Waterfox: [Classic]Waterfox has a IPC Multiprocess handle leak (and i don't know how far it goes back)

[Squall-Leonhart]

When dom.ipc.processCount is set high enough that processes are created and closed as you open and close tabs, the parent process is not destroying handles related to those content processes leading to eventual handle exhaustion. This also manifests as excessive working set consumption (up to several gigabytes)

To Reproduce

1. Set dom.ipc.processCount higher than default (lets say 7-12)
2. Navigate to the waterfox reddit
3. Note the current handle count
4. Open every post on the page.
5. Note the new handle count.
6. Close every tab except the reddit main page then change pages
7. Note the handle count again.
8. Open every post again

Result: Handles will go up and down with use, but they will always be stuck higher after IPC processes are created and destroyed several times, this indicates the presence of a handle leak as every handle relevant to the creation content process should be tracked and destroyed upon the sub processes termination.

Expected behavior
Appropriate destruction or handles.

Screenshots

• Device:
• OS: Windows 7, 8, 10
• Version: Classic 2020.09 (I do not know how far this goes back)

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[Squall-Leonhart]

This appears to be an ancient bug in Firefox that has never been fixed, i just replicated it in Firefox 81